Question

A strip footing (8 m wide) is designed for a total settlement of 40 mm. The safe bearing capacity(shear) was 150 kN/$m^2$ and safe allowable soil pressure was 100 kN/$m^2$. Due to importance of the structure, now the footing is to be redesigned for total settlement of 25 mm. The new width of footing will be

• A. 5 m
• B. 8 m
• C. 12 m
• D. 12.8 m

Answer 1

The correct option is D 12.8 m

Width of footing = 8 m
Load per metre length of footing
P = 8 $\times$ [min of bearing capacity and allowable soil pressure]
= 8 $\times$ [min {150, 100}]
= 8 $\times$ 100
= 800 kN/m
Allowable pressure for 40 mm settlement
= 100 kN/$m^2$
$\therefore$ Allowable pressure for 25 mm settlement
$=\frac{100}{40}\times 25$

Load resisted = width $\times$ allowable pressure
$\Rightarrow$ 800 = B $\times$ 62.5
$\Rightarrow$ B = 12.8 m